ABSTRACT

Infectious pathogens threaten wildlife populations through effects on host growth, reproduction, and survival. The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd), the cause of the disease chytridiomycosis, has been implicated in worldwide declines of amphibian populations. Documenting conditions under which amphibians are threatened by Bd will allow us to pinpoint at-risk populations, especially in the midwestern United States, an understudied region. We investigated how distributions of Bd differ across host life stages, land cover types, and spatial extents in a susceptible temperate host, the American Toad (Anaxyrus americanus). We surveyed a total of 232 adults at 14 sites and 430 metamorphs at 15 sites in southwestern Ohio, USA, and analyzed associations among land use type, Bd prevalence, and Bd load by using model selection. We found Bd infection prevalence in metamorphs was dramatically lower than in adults; only 1.6% of metamorphs were infected compared with 28.0% of adults. These results suggest that Bd transmission occurs after metamorphosis in this species or that infections vary with season, given that we surveyed adults in the spring during breeding events and metamorphs in the summer as they emerged from ponds. In adults, infection prevalence was reduced with increasing open-canopy habitats across spatial scales (from 100 to 1,000 m), whereas infection load increased with the proportion of forested habitats at small spatial scales (100 m). Our study shows that Bd infection risk in a temperate system can be influenced by host life stage and land cover types across local spatial scales.